Did you update your drivers recently. If so then try older ones. Check with cpuz to see if anything on your board is off like CPU overclocked or under or ram speed changed or even if the chip set is a bit off. Look at voltage and also see if there is anything you changed when this started happening. I think there was a new flash update recently. Maybe install the older one and see if that helps. Adobe is increasing the GPU usage of their flash player more now and this could cause issues sometimes. If all this fails and everything seems good then yes I'd replace the board.
Thanks for the info, but seems downgrading the flash player did the trick